Static convergence magnet for tricolor kinescope



March 14, 1961 B. R. CLAY EI'AL Filed Dec. 51. 1956 STATIC CONVERGENCE MAGNET FOR TRI-COLOR KINESCOPE 2 Sheets-Sheet 1 March 14, 1961 B. R. CLAY ETAL 2,975,314

STATIC CONVERGENCE MAGNET FOR TRI-COLOR KINESCOPE Filed Dec. 31, 1956 2 Sheets-Sheet 2 INVEN T012: Burro/v P. C2, 5 BY (k/124i: 4 67mm WLZMZ 4/ United States Patent STATIC CONVERGENCE MAGNET FOR TRI- COLOR KINESCOPE Burton R. Clay, Woodbury, and Charles E. Small, Pennsauken, N.J., assignors to Radio Corporation of America, a corporation of Delaware Filed Dec. 31, 1956, Ser. No. 631,892

12 Claims. (Cl. 31377) The invention is directed to the control of electron beams and particularly to means for providing control for the convergence of a plurality of electron beams. The invention is applicable to color television tubes and the like.

Cathode ray tubes having a plurality of electron beams may utilize a structure for positioning each beam independently of the other electron beams in the tube. Cathode ray tubes used for color television viewing tubes, as well as plural beam tubes used in oscillograph Work, often require the independent control of each electron beam so as to provide accurate positioning of each electron beam at the tube screen. Such control of the elec-- tron beams is used in plural beam color television picture tubes in order to have accurate convergence of the electron beams at the screen, as Well as to maintain beam convergence, as the several beams are simultaneously scanned over the tube screen. In such applications, magnet structures have been positioned adjacent to the path of each electron beam to provide control of the beam position during tube operation. Such magnet structures include field producing devices for moving each electron beam independently in a radial direction toward and away from the tube axis.

It is therefore an object of this invention to provide an improved magnet structure for obtaining independent control of electron beams in a plural beam tube.

It is another object of the invention to provide a novel and inexpensive magnet control means for each beam of a plural beam tube.

It is another object of the invention to provide a novel magnet control means for providing independent radial deflection control of each beam of a plural beam tube.

The invention is an improvement in the convergence deflection magnet assembly of a plural beam color tube in which permanent magnet means are utilized in combination with a U-shaped magnet core. The magnet assembly includes a plurality of magnets with each magnet in operative relationship to one of several U-shaped core members. Each magnet is adjustably mounted so hat it can be moved between the legs of its respective U-shaped core member. Movement of the magnet from one leg of the core member to the other, reverses the polarity of the legs of the core member. The magnet assembly, when mounted on a plural beam tube in its appropriate position, provides radial control of each electron beam, and the adjustment of the magnet position determines the static positioning of the electron beam relative to the tube axis.

Figure 1 is a schematic showing of a plural beam tube utilizing the invention.

Figure 2 is an enlarged partial sectional view of Figure 1 along lines 2-2 of Figure 1.

Figure 3 is a partial view of a detail of Figure 2 along the lines 3-3 of Figure 2.

Figures 4 and 5 are views of a modification of the invention.

Figure 1 shows a cathode ray tube utilized for color 2,975,314 Patented Mar. 14, 1961 television. The tube envelope consists of a bulb portion 10 and an axially aligned neck portion 12 fixed thereto. Bulb portion 10 is closed with a glass face plate 14-, on the inner surface of which is formed a phosphor screen 16 which luminesceses with different colors of light when struck by high energy electrons. The neck portion 12 of the envelope is hermetically closed at its free end, to which is fixed a base 18 with the conventional lead pins 20 for connecting electrodes within the tube to appropriate sources of potential. Mounted within the tube neck 12, and only schematically represented, is an electron gun structure 22 for providing three electron beams which are directed and focused by the gun structure 22 onto the phosphor screen 16. The electron gun structure is not shown in detail but may be of any conventional design for providing three independent electron beams.

The electron beams are brought to convergence near an apertured masking electrode 24 closely spaced from the phosphor screen 16. Since the electron beams are spaced within the region of gun 22, the beams approach the mask 24 from different directions when they are converged at the masking electrode 24. Thus, the beam portions passing through the apertures of electrode 24 will diverge and strike different areas of the phosphor screen. The three electron beams are simultaneously scanned over the surface of electrode 24 by conventional scanning fields provided by pairs of coils formed into a yoke structure 26 mounted around the tube neck 12. Electron beams are scanned in any well known raster configuration, such as a rectangle having a 3:4 aspect ratio. Those areas of the phosphor screen 16, which are struck by electrons from one beam are coated with a phosphor material producing light of one color under electron bombardment. Areas of the phosphor screen 16 struck by electrons of a second electron beam are coated with a phosphor material emitting a second color light under electron bombardment while the areas of the screen struck by electrons of the third beam are coated with a third phosphor material emitting light of a third different color under electron bombard ment. The three beams, upon being scanned over the screen 16, thus, each causes a diilerent colored light to be produced. Appropriate modulating signal potentials applied to the gun structure 22 will provide a single picture in color. All details of the construction and operation of the color tube of Figure l are well known and since they do not constitute a part of this invention, they are not described in greater detail.

The three electron beams formed by the gun structure 22 may originate as parallel beams, which are subsequently brought to convergence at the apert-ured mask 24, or the three beams may be initially directed to the point of convergence on electrode 24 as non-parallel converging beams by the electron gun structure 22. In either case, it has been found that means for controlling each electron beam, independently of the others, is nec essary to, either converge the beams or to provide correction of the beam convergence.

Figure 2 discloses a structure for providing convergence control of each electron beam independently of the other beams. In Figure 2, the three electron beams are schematically represented by the circles 23, 3t and 32. These circles represent the sectional areas of the respective beams, which can be thought of running in and out of the plane of Figure 2 and substantially normal thereto. Mounted within the tube neck structure 12, are a plurality of pairs of magnetic pole pieces. One pair of pole pieces 34 and 36 respectively are positioned on opposite sides of beam 28. A second pair of pole pieces 38 and 40 are positioned on opposite sides of beam 36, while a third pair of poles pieces 42 and 44 are positioned on opposite sides of the electron beam 32. Each pair of pole pieces has parallel portions, between which the respective electron beam passes. All of the pole pieces have a portion extending away from its parallel portion and along the wall of the tube neck 12. These portions of the pole pieces extending along the glass neck 12 are represented by the reference numerals 34, 36, 38', 40, 42' and 44, respectively.

Mounted 011 the tube neck 12 are three U-shaped permeable magnetic cores 46, 48 and 50. Core 46 has a pair of leg portions 52 and and 54, the ends of which are positioned adjacent to-the glass neck 12 and on opposite sides of the neck from plate portions 34' and 36' respectively. Similarly, core 48 has a pair of leg portions 56 and 58, the ends of which are positioned close to the glass neck 12 and immediately on the opposite side of the neck 12 from pole piece portions 38' and 40' respectively. And, also, core 50 has leg end portions 60 and 62 positioned on opposite sides of the neck 12, from pole piece portions 42 and 44'. These end portions of. each of the U-shaped magnetic cores are in this manner closely coupled to the respective pole piece portions closely spaced from them within the tube neck 12. The ends of the legs of each U-shaped member are fitted into apertures of a plastic support 78, which is fitted in contact with the tube neck 12. The ends of the core members do not pass entirely through the respective supports 78 and thus do not contact the glass neck 12. The members 78 are fitted together at the ends to form a triangular support assembly as shown in Figure 2. This support assembly is not part of the invention but a similar one is described and claimed in U.S. patent application 531,940, filed by Lazzery on September 1, 1955 now Patent No. 2,864,021, granted December 9, 1958. The plastic support members 78 are held in their assembled inter-fitted relationship by spring clips 80 fixed within apertures formed in adjacent ends of each support member 78. Cores 46, 48 and 50 are held in position on their respective support members 78 by leaf springs 79, each fixed at one end to an integral stud 67 of support 78 and contacting the respective core member, at its other end. Surrounding the legs of each U-shaped core member is a magnetic coil 64 for producing a magnetic flux, which has a path around the respective U-shaped core member into the pair of pole piece structures coupled to the respective legs of the core and across the space between the parallel portions of the pair of pole pieces. -A magnetic field passing in a direction normal to each pair of parallel pole piece portions will cause the electron beam passing between the parallel pole piece portions to be moved either toward the axis of the tube neck 12 or radially away from it. The direction of radial movement of each electron beam depends upon the direction of the magnetic flux between the parallel pole piece portions between which the beam passes. Also, the amount of radial movement of each electron beam depends upon the strength of the magnetic field passing between the prospective parallel plate portions.

The structure of Figure 2 is utilized in plural beam tubes for controlling the radial position of each electron beam independently of the other beams. In plural beam picture tubes used for color television for example, and of the type using three electron beams and as described above relative to Figure 1, the three electron beams are converged in a common point on the apertured mask electrode 24. As the electron beams are scanned over the mask electrode 24, convergence at the mask of the three beams is lost, and to retain constant convergence of the three beams at the mask 24, a dynamic correction must be applied to each electron beam. Constant convergence of the three beams is maintained by providing at each instant, during the simultaneous scanning of the electron beams, a radial deflection to each beam in an amount determined by the amount of deflection provided by the scanning yoke 26 of the three beams from the center of screen 16. For this purpose, during tube opera tion, a varying dynamic current is passed through each coil 64 and which is of appropriate strength and direc tion to provide the required radial correction to the re spective beam.

The above dynamic convergence of the three beams, during simultaneous beam scanning, is possible, if the three beams are first converged statically at the center of the apertured mask 24, since the amount of dynamic convergence correction applied to each electron beam during scanning is dependent upon accurate static convergence of the electron beams.

Therefore, in accordance with the invention, Figure 2 discloses a novel structure for producing static con vergence of the three electron beams. This structure includes a permanent magnet 70 mounted adjacent to the core leg ends 52 and 54 of core 46, a second permanent magnet 72 mounted adjacent to the core leg ends 56 and 58 of core 48, and the third magnet 76 mounted adjacent to core leg ends 60 and 62 of core 50. The several magnets 70, 72 and 76 are fixed respectively to nonmagnetic threaded rods 82, 84 and 86. As shown in Figure 3, specifically with respect to threaded rod 82, each magnet, such as the magnet 70, shown, has a slot 88 therethrough fitted to a reduced portion of the threaded rod 82. Each of the threaded support rods 82, 84 and 86 is mounted on a brass plate 90 fixed by any appropriate means such as screws 92 to the respective plastic support member 78. The threaded rods 82, 84 and 86 are rotatably fixed to their respective plates 90 by passing the rods through apertured ear portions 94 and 96 respectively. Supporting cars 96 fit the threaded portion of each of the support rods so that upon turning the rod about its longitudinal axis the threaded portion will move the respective rod along a longitudinal path relative to its length. In this manner, the magnet will be moved from a position close to one leg end of the U-shaped core member, adjacent to which it is mounted, to a position close to the other leg end of the core member.

Magnet 70 is shown, by way of example, as being positioned adjacent to the leg end 52 of core member 46. If the upper surface of the magnet 70 is considered north and the bottom surface south, a flux path is introduced in the core 46 and in the direction represented by the arrows shown. That is, the flux path would extend upwardly, across the U portion of core 46, and downwardly through the core end 54. Since plate 36 is closely coupled by portion 36' to core end 54, the flux will pass through the glass of neck 12 into plate portions 36' and 36, across the intervening space between the parallel portions of plates 36 and 34, through plate 34 to its portion 34', which is coupled to the core end 52. The direction of the field then, between parallel plate portions 34 and 36 is in the direction of the arrow shown, and extends from plate 36 to plate 34. A magnetic field in this direction will move electron beam 28 radially away from the axis of the tube neck 12.

The position of the permanent magnet 72 is shown as being adjacent to leg end 58 of core 48. The flux established in core 48 is now in the direction of the arrow shown and thus substantially in the opposite direction to the flux direction in core 46. The direction then, of the magnetic field resulting from the position of magnet 72 would be from parallel pole piece plate portion 38 to plate portion 40 and in the direction of the arrows therebetween. The effect on the electron beam 30 of this magnetic field is to urge the electron beam radially toward the axis of the tube neck 12.

The position of magnet 76 is that which is equally spaced between the leg ends 60 and 62 of core 50. Here, there is substantially no efiective flux path through core 50 nor between the parallel pole piece plate structures 42 and 44. Accordingly, electron beam 32 would have no radial deflection placed upon it.

Adjustment of permanent magnets 70, 72 and 76 enablesthe displacement of the respective electron beam in a radial direction either toward or away from the axis of the tube neck 12. With this structure then, the three electron beams may be accurately brought toconvergence at the mask electrode 24. Also, the position of any one of the electron beams relative to the axis of the tube neck 12 may be accurately controlled.

Figures 4 and 5 disclose a modification of the invention and prime numbers are used to designate structures similar to corresponding structures in Figure 2. In Figure 4 only a single plastic support member 78 is shown. A magnet core 46 (shown in phantom) may be mounted on the support member 78 with core end portions 52 and 54 extending into apertures of the support 78'. A magnet coil 64 (shown in phantom) may be mounted around the legs of the U-shaped core piece 46'. The core 46' may be held onto the support member 78 by the spring clip 79 fixed to a stud 67' integral with support member 78. The permanentmagnet used for radial beam correction is a small magnet 70 fixed to a metal support member 100. A pair of lugs 102 integrally formed from mount member 78 support the metal men.- ber 100 for free sliding movement. Lugs 102 extend through an arcuate slot 104 of member 190. By means of an operating handle 106, the magnet support 100 may be moved on the support lugs 102. Magnet 70' is held by fingers 108 projected from member 100 and which enclose the magnet to firmly fix it to the slide member 100. The magnet 70' then may be manually positioned by means of the slide member 100 between the legs of the U-shaped core member 46'. In this manner the flux path through the core member 46 and the corresponding internal pole piece structure within the tube may be varied both as to direction and degree and in the manner described above.

What is claimed is:

l. A magnet assembly comprising a. magnet and a pair of pole pieces spaced from each other, means mounting said magnet adjacent to said pole pieces to form a magnetic field therebetween, said magnet mounting means including a threaded screw supporting said magnet for adjustably moving said magnet from a position adjacent to one of said spaced pole pieces to a position adjacent to the other of said spaced pole pieces for varying said magnetic field.

2. A magnet assembly comprising a magnet and a pair of pole pieces spaced from each other, means mounting said magnet adjacent to said pole pieces to form a magnetic field therebetween, said magnet mounting means including a bolt passing through said magnet for adjustably moving said magnet from a position adjacent to one of said spaced pole pieces to a position adjacent to the other of said spaced pole pieces for varying said magnetic field.

3. A magnet assembly comprising a magnet, a magnetically permeable core having a pair of spaced end portions, means mounting said magnet adjacent to said core, said magnet mounting means including structure for adjustably moving said magnet from a position adjacent to one of said core end portions to a position adjacent to said other core end portion.

4. A magnet assembly comprising a magnet, a mag netically permeable core having a pair of spaced end portions, means mounting said magnet adjacent to said core, said magnet mounting means including a threaded rod for adjustably moving said magnet from a position adjacent to one of said core end portions to a position adjacent to said other core end portion.

5. A magnet assembly comprising a magnet, a U-shaped magnetically permeable core with spaced end portions, means mounting said magnet adjacent to said core end portions, said magnet mounting means including structure for adjustably moving said magnet across said U- shaped core from a position adjacent to one of said core end portions to a position adjacent to said other core end portion.

6. A magnet assembly comprising a magnet, a U- shaped magnetically permeable core with spaced end portions, means mounting said magnet adjacent to said core end portions, said magnet mounting means including a threaded rod supporting said magnet for adjustably moving said magnet from a position adjacent to one of said core end portions to a position adjacent to said other core end portion, said threaded rod being mounted across the end portions of said U-shaped core whereby said magnet may be adjustably moved therebetween.

7. In beam convergence apparatus including a mount having a cylindrical aperture, and a magnetically permeable core member having spaced end portions, said core member being supported on said mount with said spaced end portions disposed in the vicinity of said aperture, static convergence field producing structure comprising the combination of means including a permanent magnet supported on said mount in proximity to said core mem her for developing a magnetic field within said aperture between said spaced end portions, and means for varying the strength of said magnetic field, said last-named means comprising means for altering the position of the center of gravity of said magnet within a plane perpendicular to the axis of said cylindrical aperture.

8. Apparatus in accordance with claim 7 wherein said position altering means comprises a movable holder for said magnet for controllably varying the distance between said magnet and one of said spaced end portions.

9. Apparatus in accordance with claim 8 wherein means are provided for constraining movement of said movable holder to movement in two mutually opposite directions, movement in one of said two directions increasing the distance between said permanent magnet and said one end portion and decreasing the distance between said permanent magnet and the other of said end portions, and movement in the opposite direction decreasing the distance between said permanent magnet and said one end portion and increasing the distance between said permanent magnet and said other end portion, the

range of movement in said two directions being sufficient to achieve control of the polarity of said magnetic field by means of movement of said movable holder.

10. In beam convergence apparatus including a mount having a cylindrical aperture, and a plurality of magnetically permeable U-shaped core members each having spaced end portions, each of said core members being secured to said mount in a difierent radial position with respect to the axis of said cylindrical aperture and with the spaced end portions thereof disposed in the vicinity of said aperture, apparatus for effecting static convergence comprising the combination of a plurality of permanent magnets, each of said permanent magnets being positioned in proximity to a diiferent one of said plurality of core members for developing a respective magnetic field within said aperture between the spaced end portions of the respective core member, and means for varying the strength of each of said respective magnetic fields, said last-named means comprising means including a slidable holder for each of said permanent magnets for altering the position of the center of gravity of the respective magnet within a plane perpendicular to the axis of said cylindrical aperture.

11. In beam convergence apparatus for use with a multi-beam cathode ray tube having a neck, said convergence apparatus including a support having a cylindrical central opening adapted to receive the neck of said cathode ray tube, and a plurality of magnetic permeable U-sh-aped core members each having spaced legs, each of said core members being secured to said support with its legs disposed generally parallel to a respectively different radius of said cylindrical opening and oriented with the free ends of its legs toward said opening, static convergence field producing structure comprising the combina tion of a plurality of permanent magnets, each of said permanent magnets being disposed in proximity to a respectively different one of said core members for developing an individual magnetic field within said aperture between the free ends of the legs of the respectively associated core member, and means including a slidablc holder for each of said permanent magnets for moving the center of gravity of each said magnet within a plane perpendicular to the axis of said cylindrical opening whereby to provide an individual control of the strength of each of said magnetic fields.

12. Apparatus in accordance with claim 11 wherein means secured to said support are provided for retaining each of said magnet holders such that inovem'entof each of said magnets alters the distance between said magnet and the free end of one of the spaced legs of the respectively associated core member.

' References Cited in the file of this patent UNITED STATES PATENTS 2,743,389 Guiffrida Apr. 24, 1956 2,761,989 Barkow Sept. 4, 1956 2,763,804 Morrell Sept. 18, 1956 2,766,393 Casey Oct. 9, 1956 2,791,709 Landes et a1. May 7, 1957 

